Since HER2 abnormality is very common in breast cancer, the current National Comprehensive Cancer Network (NCCN) guidelines and Chinese Society of Clinical Oncology (CSCO) guidelines clearly recommend that HER2 testing should be conducted for breast cancer therapy, comprehensively determined by combining HER2 protein level (immunohistochemistry) and amplification level (fluorescence in situ hybridization/sequencing). The gene discussed is ERBB2; the disease is breast cancer.